1. Field of the Invention
The present invention is directed to a process for preparing tetraalkyl butanetetracarboxylates by electrolytic hydrodimerization of dialkyl maleates in alkanols.
The compound 1,2,3,4-butanetetracarboxylic acid has been found by the U.S. Department of Agriculture to be an effective permanent press agent for polycotton fabrics, and the compound could find use in large quantities for such purpose. Accordingly, an efficient process for preparing the compound could be very useful. Such a process must produce a product of acceptable color performance properties, as this is an important factor for suitability for permanent press agents. The electrolytic process of the present application produces the tetraalkyl 1,2,3,4-butanetetracarboxylates, and such compounds can be converted to 1,2,3,4-butanetetracarboxylic acid, as described and claimed in our commonly assigned copending application Ser. No. 07/450,760 Case 43-21(7833).
2. Description of the Related Art
Electrolytic reductive couplings of various activated olefins have been investigated and reported in the past. Much of this work involved aqueous systems in a divided cell, and often with a supporting electrolyte salt with a very negative discharge potential, such as a quaternary ammonium salt. In addition to reductive couplings, other reactions such as simple reduction and polymerization frequently occur. Various parameters of such reactions have been discussed, including use of various electrolytes, see Organic Electrochemistry, edited by Manuel M. Baizer and Henning Lund (1983, Marcel Dekker, N.Y., N.Y.). At page 669 of this reference, it is stated that undivided cells are operable with the restrictions that (1) the olefin and product not be substantially oxidized at the anode, and (2) the oxygen evolved at the anode in aqueous systems not promote undesirable side reactions. This reference also refers, for example at pages 669 and 672, to dimerization of diethyl maleate and the effect of alkali metal cations in increasing the rate of dimerization of anion radicals.
Electrolytic hyrodimerization of diethyl maleate has been reported by Baizer and Petrovich, J. Electrochem. Soc., 114 (10), 1024-1025 (1967); the described procedures utilized a catholyte of water and dimethylformamide in a divided cell and indicated, all other conditions being the same, more hydrodimerization occurs in the presence of tetraethylammonium ion than of sodium ion. The electrolyses were carried out for three (3) hours, generally resulting in about 50% conversions, and specified amounts of hydrodimer, and other products.
Methanol has been used as a solvent for study of reduction mechanisms. See Dimitra Sazou et al, "Electrochemical Reduction of Maleic and Fumaric Acids and Their Dimethyl Esters in Methanol at a Mercury Electrode", Dimitra Sazou et al, Coll. Czech. Chem. Comm., 52, 2132-2141 (1957). Cyclic voltammograms of the acids in methanol solution with various supporting electrolytes, employing a hanging mercury drop electrode, are given, and reduction mechanisms discussed. The double bond reduction of the corresponding dimethyl esters was stated to take place in one step. The described procedures utilized very dilute solutions of the acids, e.g. 0.0025 or 0.005 moles per liter.